A flat panel virtual-pinhole PET insert for axillary and internal mammary lymph node imaging in breast cancer patients

Objectives A flat panel PET insert is currently being developed with the goal of imaging axillary and internal mammary nodes in breast cancer patients. This insert is based on the “virtual pinhole PET” (VP-PET) principle, and works in conjunction with a whole body PET scanner to provide whole body images with enhanced spatial resolution in the area close to the insert.

Methods The proposed panel consists of 28 detectors arranged in a 7 x 4 array. Each detector module consists of a silicon photomultiplier (Hamamatsu S11064) coupled to a 20 x 20 LYSO crystal array (0.8 x 0.8 x 3 mm³) via a custom light guide. The panel has an imaging area of approximately 12.0 x 7.5 cm². The flat panel detectors will be integrated into a Siemens Biograph 40 Whole Body PET-CT scanner to generate images.

Results With a prototype half-ring VP-PET insert developed previously in the laboratory (consisting of 13 x 13 LYSO array each 2 x 2 x 5 mm³ coupled to MA-PMT), phantom studies have shown an improvement in the spatial resolution from 4.3-5.5 mm to 2.4-3.0 mm within a whole body PET scanner. Based on these results, we expect a spatial resolution of less than 2 mm using the proposed new system. The design and phantom studies evaluating the performance characteristics of the flat panel insert will be presented.

Conclusions The feasibility of the VP-PET approach has been established, and we are now extending this principle to a more modular and flexible design by using flat panel geometry. Such geometry can be easily positioned against any region of interest to be imaged with high resolution while maintaining whole body imaging capability and can be particularly beneficial in evaluating lymph node status in breast cancer patients